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Full text of "Dissection of the platana and the frog"

THE FIELD MUSEUM LIBRARY 



3 5711 00004 4355 




1 




UNIVERSITY OF CAPE TOWN 



2ctologtral ifeparttnent 



DISSECTION OF 



The Platana and the Frog 



-BY 

J. D. F. GILCHRIST. M. A.. DSc, Ph.D. 

Professor of Zoology in the University of Cape Town, 
AND 

C von BC5NDE, M.A., 

Lecturer in Zoology in the University of Cape Town, 




919. 



CAPE TIMES LIMITED, CAPE TOWN. 



UNIVERSITY OF CAPE TOWN. 



Znolngtral Sfpartment 



DISSECTION OF 

The Platana and the Frog 



BY 

J. D. F. GILCHRIST, M.A., D.Sc, Ph.D., 

Professor of Zoology in the University of Cape Town, 
AND 

C. von BONDE, M.A., 

Lecturer in Zoology in the University of Cape Town. 




1919. 

CAPE TIMES LIMITED, CAPE TOWN. 



0L- 

.: 



NOV 1 3 |g 4 g rye. 



PREFACE AND INSTRUCTIONS. 



OWING to the fact that some of the types of animals available for 
the study of Zoology in South Africa differ from those de- 
scribed in text books for students in other countries, it has been 
found necessary to draw up special directions and diagrams for 
laboratory use in this country. These are now put in the more 
convenient form of a text book, which, though intended primarily 
for the use of the students of the University of Cape Town, may, 
it is hoped, prove useful to others engaged in the teaching and 
study of Zoology in South Africa. 

The general plan of the course intended to be followed is first 
an introductory study of a type of vertebrate. The Platana or 
Clawed Toad, Xenopus leer is, is the most convenient type for this in 
South Africa and in some respects is more instructive than the Frog. 

Xenopus is therefore chiefly dealt with, but Rana can also be 
used, the differences in this type being indicated in italics. It is 
recommended that both types be studied where possible. 

Only these two types are dealt with here, but may be followed 
by descriptions of other South African types, such as the South 
African Crawfish, Dogfish, Earthworm, etc. 

It is intended that the student should make drawings of his dis- 
sections on the blank page. He should not copy the diagrams, but 
draw what he actually sees, and be prepared to demonstrate the 
parts to the teacher. 

The instruments required are a large and a small pair of 
scissors, a large and a small scalpel, moderately fine forceps, a 
seeker, and pins. 

We are indebted to j\lr. W. von Bonde, M.A., for the drawing 
of Figs. 3-5, 7-10. 

J. D. F. G. 

Zoological Laboratory, C. v. B. 

University of Cape Town, 
June, 1919. 



Digitized by the Internet Archive 
in 2013 



http://archive.org/details/dissectionofplatOOgilc 



THE PLAT ANA (Xenopus Icevis). 

THE FROG (Bana fuscigula): 



First Day. 



External Characters. 

1. Make a drawing of the animal viewed from above, showing : — 

(a) The nostrils. 

(b) The eyes. 

(c) The nictitating membrane and a short tentacle beneath the 

eye. [The tentacle is absent in the Frog.] 

(d) The tympanic membrane, which is not shown in the Platana, 

but is well marked in the Frog. 

(e) The opening of the cloaca. 
(/) The limbs and their divisions. 

(g) The skin with tube-like lines round the body. [In the Frog 
these lines are not present.] 




Fig. 1. — Xenopus lasvis and Rana fuscigula. 



2. Make an enlarged drawing, about twice the natural size, showing : — 

(a) The fore-limb with the digits. 

(b) The hind-limb with the digits. The inner three digits have 

claws, j The claws are absent in the Frog.] 

Name the parts of these limbs, and number the digits from within out- 
wards, noting that the first is absent in the fore-limb. 



Mouth Cavity. 

Open the mouth cavity widely, and make a sketch showing : — 

(a) The teeth on the upper jaw. 

(b) There are no teeth on the vomer. [In the Frog each vomer is 

supplied with teeth.] 

(c) The internal openings of the nostrils. 

(d) The single opening of the Eustachian tubes. [In the Frog there 

is an opening on each side.] 

(e) There is no tongue. [A tongue is present in the Frog.] 
(/) The glottis. 

(g) The gullet. 

Owing to the complexity of the Eustachian tubes and the bony form 
of the ear cavity, it is not possible to pass a seeker from the Eustachian 
aperture through the tympanic membrane. [In the Frog the Eustachian tubes 
are short and straight and permit of this being done.] 



Vomerine teeth 




Teeth on Upper Jaw 
Internal nares 



Eustachian aperture 
— • Gullet 



Glottis 



Tongue 

Fig-. 2. — Month cavity of Xenopus and Rana. 




Teeth on Upper Jaw 
Internal nares 



Eustachian aperture 

Gullet 



Glottis 



Muscular System and Vascular System (Part). 

1. Pin the Platana on its back in water, and cut through the skin with 
scissors along the middle line, throughout the whole length of the body. 
Pin back the skin on each side, and make a drawing showing : — 

(a) The muscles : 

(i) Two pectoralis muscles passing from the base of the arm, the 
one to the middle line of the body, and the other over the 
abdominal region to the posterior part of the body. Cut 
through this latter muscle at its anterior end, and fold it back- 
wards to expose the underlying brachial vein. 

(ii) The rectus-abdominis muscles passing along the mid-ventral 
line of the body, with the white line (linea alba) in the centre. 

(hi) The deltoid muscle to the arm. 

(iv) The mylo-hyoid muscle, on the underside of the mouth region. 
(v) The obliquus-externus muscle, lying under the second pectoralis 
muscle noted above. 



(b) The cutaneous and the muscular veins, lying under the pectoralis 

muscle, and arising independently from the subclavian vein. They 
supply the skin and muscles in the region of the arm. There is a 
second cutaneous vein arising from the abdominal vein and extend- 
ing on to the skin of the abdomen. Two other small cutaneous 
veins are seen on the skin of the leg, and another on the skin under 
the mouth. 

[In the Frog a single musculo-cutaneous vein is seen lying under 
the pectoralis muscle and extends on to the skin.] 

(c) The abdominal vein, partly visible through the wall of the body, in 

the centre of the rectus-abdominis muscle. 

(d) The brachial vein going to the arm, near which may often be seen 

the white brachial nerve. Endeavour to trace the point of origin 
of the brachial, muscular, and cutaneous veins (or the brachial and 
musculo-cutaneous veins in the Frog) as shown in the figures. 



Mylo-hyoid 




Fig. 3. — Muscular System and Vascular System (part) of Xenopus and Rana. 



2. Make an incision in the body wall, slightly to the right side of the 
abdominal vein, which may now be seen clearly on the inner side of the 
body wall. Carefully detach this vein from the abdominal wall. 



Second Day. 



Skeletal System (Part). 

1. Remove the pectoralis muscles covering the body between the arms 
to show the bones of the central part of the shoulder girdle and sternum, 
viz. : — 

(a) The thick coracoids. 

(b) The more slender clavicles anterior to them, both extending from 

the base of the arm on each side towards the centre of the body. 

(c) The sternum, consisting of a median row of cartilages which are 

believed to be derived from the shoulder girdle. It does not, there- 
fore, correspond to, or is not homologous with, the sternum of the 
Pigeon or the Rabbit, which is derived from the ribs. The sternum 
consists of the following parts : 

(i) The two epicoracoids consisting of cartilage. 

(ii) The metasternum which is broad and consists of cartilage only. 




osternum 

trnum 



Epicoracoid 




Coracoid 



Epicoracoid 

Sternum 

Xiphisternum 



Fig. 4. — Pectoral Girdle of Xenopus and Rana. 

[In the Frog the sternum is composed of the following parts : — ■ 

(i) The omosternum consisting of tivo parts, an anterior cartilaginous 
part (sometimes called the omosternum) and a posterior bony part 
(sometimes called the episternum). 

(ii) The two epicoracoids consisting of cartilage, 

(Hi) The metasternum consisting of two parts, an anterior bony part 
(sometimes called the sternum) and a posterior cartilaginous part 
(sometimes called the xiphisternum).'] 

Make a sketch of the pectoral girdle. 



10 



2. Cut through the coracoids and clavicles on each side, close to the 
base of the arm, and carefully remove this part of the pectoral girdle and 
sternum so as to show the heart lying underneath. 



Rllihi auricle 
Ventricle 





Fig-. 5. — Dissection of Xenopus and Rana to show the Alimentary System, etc. 



Alimentary System. 

Make a sketch showing : — The heart, lungs, liver, gall bladder and bile 
duct going to the duodenum, exposed parts of the stomach, duodenum, 
small intestine (or ileum), large intestine, urinary bladder, pancreas, and 
spleen. 



12 



Third Day. 



Vascular System (continued). 
A. Venous System. 

1. Note :— 

(a) The heart lying in the thin pericardium, the two auricles, the single 

ventricle, the truncus arteriosus which divides into two branches. 
Remove the pericardium from the heart, and tilt the apex of 
the heart forwards, noting the sinus venosus into which the right 
and the left superior vena? cava? (or precavals) and the single inferior 
vena cava (or postcaval) open. 

(b) The veins passing from each side of the sinus venosus. Each superior 

vena cava is joined by the following branches : — 

(i) The external jugular vein from the region of the tongue and 
the mandible. 

(ii) The internal jugular vein from the head and a thick subscapular 
vein from the shoulder. These veins join the superior vena 
cava independently of each other so that there is no innominate 
vein as in the Frog, 
(hi) The subclavian vein, made up of a brachial vein from the arm, 
a cutaneous vein from the skin, and a muscular vein from the 
abdominal muscles. The cutaneous and the muscular veins 
are separate veins so that there is no single musculo-cutaneous 
vein. 
[In the Frog the superior vena cava is joined by the folloiving branches : — 

(i) The external jugular vein, formed by the union of a lingual vein 
from the tongue and a mandibular vein from the margin of the 
lower jaw. 

(ii) The internal jugular vein from the head and the subscapular vein 
from the back of the arm and shoulder, both joining the superior 
vena, cava by a common vein, the innominate. 

(Hi) The subclavian vein, formed by the brachial vein from the fore- 
limb and a musculo-cutaneous vein from the muscles of the body 
and from the skin.~\ 

(c) The hypoglossal and the glossopharyngeal nerves, both running 

alongside of the lingual artery. 
Make an enlarged drawing showing the above parts (a) and (b). 

2. Note the inferior vena cava, receiving the renal veins from the kidneys, 
the hepatic veins from the liver, and opening into the sinus venosus. 

3. Trace back the abdominal vein, and note that it is formed by the 
union of the two pelvic veins, which pass along the bases of the legs. The 
pelvic veins occur deep down in the body under the posterior part of the 
pelvic girdle, which should be cut through in order to see them. At the 
union of the pelvic veins to form the abdominal vein a small rectal vein, 
passing along the ventral surface of the rectum, joins the abdominal vein. 

14 



In order to make out the femoral and the sciatic veins, turn the Plat ana 
over and remove the skin from the back of the leg. The femoral vein may 
then be seen lying on the surface of the leg, between two of the muscles. 
By carefully separating these muscles the whole of the femoral vein may 
be exposed. Deeper down in the muscles of the leg lies the sciatic vein, 
and, between the sciatic and the femoral veins, the internal iliac artery may 
be seen running alongside of the sciatic nerve. 

Trace the femoral and the sciatic veins forward, and note that they join 
together at the point where they meet the pelvic veins and then run forward 
to the kidney as the renal portal vein on each side. 

Turn the Platana over again on to its back and note the renal portal 
vein from the ventral side. Joining the renal portal vein is a large vein 
formed of two branches. The one branch arises in the abdominal wall, 
while the other passes along the base of the leg and joins the abdominal 
vein. On each side three dorso-lumbar veins join the renal portal vein. 




Fig-. 6.— Venous System of Xenopus and Rana. 

[In the Frog the abdominal vein is also formed by the union of the two 
pelvic veins. The pelvic veins, however, lie more superficially than in the 
Platana. The femoral vein which passes along the front of the thigh divides 
into two branches, the one branch forming the pelvic vein, the other, joined by 
the sciatic vein from the muscles and shin of the bach of the thigh, forming the 
renal portal vein extending along the outer side of the hidney. The dorso-lumbar 
vein from the dorsal wall of the body joins the renal portal vein.'] 

Make a drawing showing the above parts. 



16 



B. Arterial System. 

Distend the oesophagus with a piece of cotton wool or paper to show 
the blood vessels more clearly. Trace out the anterior part of the arterial 
system, made up of two branches of the truncus arteriosus each of which 
divides into : — 

(a) The carotid arch passing to the head region. 

(b) The systemic arch curving round the oesophagus. 

(c) The pulmo-cutaneous arch to the lungs and the skin. 



18 



Fourth Day. 



Arterial System (continued). 

1. Trace the carotid arch, which gives off : 

(a) Two lingual arteries having a common point of origin near the 

carotid gland. 

(b) A carotid artery passing to the head. At its origin it is slightly 

swollen into the carotid gland. 

2. Trace the systemic arches which run backwards on each side of the 
body, meeting posteriorly to form the dorsal aorta. Each systemic arch 
gives rise to an artery which branches into :— 

(i) A scapular artery to the pectoral girdle, 
(ii) A cutaneous artery to the skin. 
(iii) A brachial artery to the arm. 
Trace the dorsal aorta backwards, and note that it gives rise to the 
cceliaco-mesenteric artery about midway between its origin and the origin 
of the first pair of renal arteries. The dorsal aorta then passes between 
the kidneys giving four renal arteries to each, and proceeds backwards and 
divides into an internal iliac artery to each leg. This artery lies between 
the femoral and the sciatic veins. From each of these arteries a branch is 
given off which divides into : 

(i) An iliac artery to the muscles around the ilium, 
(ii) A cutaneous artery to the skin of the body, just anterior to the 

leg. 
(iii) A small artery to the anterior dorsal surface of the hind limb. 

3. Trace the pulmo-cutaneous arch, which gives off : — 

(a) A pulmonary artery, running along the outer side of the whole length 

of the lung. 

(b) A cutaneous artery, which at first runs forwards to the base of the 

arm, and becomes spread out on the skin of the back of the head. 

[In the Frog 

1 . The carotid arch gives off : — 

(a) A lingual artery supplying the tongue. 

(b) A carotid artery, running round the side of the oesophagus, and 

supplying the head. At its origin it is slightly swollen into the 
carotid gland. 

2. The systemic arches run backwards on each side of the body, and meet 

posteriorly to form the dorsal aorta. Each systemic arch gives off : — 

(a) A subclavian artery to the shoulder and fore-limb. 

(b) An occipito-vertebral artery to the head and the vertebral column. 

(c) An oesophageal artery to the dorsal wall of the oesophagus. 

(d) A laryngeal artery to the larynx. 

At the point where the dorsal aorta is formed, note the origin of 
the coeliaco-mesenteric artery which sends branches to the stomach, liver, 
intestine, and spleen. 

20 



Trace the dorsal aorta backwards and note that it passes between 
the kidneys, to each of which it gives off four renal arteries and then 
it divides posteriorly into an iliac artery to each leg. The iliac artery 
is continued backwards as the femoral artery in the leg. 

3. The pulmo-cutaneous arch gives off : — 

(a) A pulmonary artery, running along the outer side of the whole 

length of the lung. 

(b) A cutaneous artery, which at first runs forwards and upwards, 

and then turns backwards, supplying the skin of the back and 
the sides of the head.] 

Make a complete sketch of the arterial system. 




Carotid gland 








I. Carotid 




l^hyrold^ 
IB gland M 


I Ungual 
Carotid gland 


Pulmocuuneous 
arch 


Pulmocutanaous V^ 
arch -^** 


_ / Carotid arch 


\^^^- Carotid 
-. ^^--Cutaneout 


^.-CutUMOut 


Pulmonary — \tXi 




|Jy X Occipito-vertehral 
*6 \aaaaaaaaaa*- Subclavian 


- ~ Pulmonary 


Lung.... (A 




M Syataroic arch 



Coellaco- mesenteric 




Fig. 7. — Arterial System of Xenopus and Rana. 



Cut out the heart, leaving attached to it as much as possible of the large 
vessels. 

Note the sinus venosus, truncus arteriosus, auricles, and ventricle. 

Open the auricles and observe the division between them and the openings 
of the veins passing into them. 

Make a section through the auricles and ventricle noting the thick muscular 
walls of the ventricle and the valves between it and the auricles. 



22 



Respiratory System and Alimentary System {continued). 

1. Remove the mylo-hyoid muscles to expose the hyoid apparatus. Pass 
a seeker through the glottis to one of the lungs and slit it open with a pair 
of scissors. Examine the structure of the lung. 

2. Remove the whole of the alimentary canal with the lungs, liver, pan- 
creas, and spleen, by cutting through the oesophagus and the large intestine 
before it joins the cloaca, and detaching it from the roof of the body cavity 
without injuring the kidneys and the reproductive organs. 

Draw the complete alimentary canal. 




Entrance of Bile duct 
into Duodenum 



Cloacal aperture 



Fig. 8.— Alimentary Canal of Xenopus and Rana. 



Urinogenital System. 

Note the kidneys, two elongated, flattened, dark-red bodies lying one 
on each side of the vertebral column towards the posterior end of the abdo- 
minal cavity. From the outer edge of each kidney a ureter arises and runs 
backward, opening into the cloaca on the dorsal side, opposite the opening 
of the urinary bladder. 

[In the Frog the adrenal bodies may be seen on the ventral sides of the kidneys 
as small yellow patches.] 



24 



In the male Platana note : — 

(a) The testes, a pair of ovoid pale-yellow bodies attached to the dorsal 

wall of the body cavity by a fold of the peritoneum. They lie 
on the ventral sides of the kidneys and are connected to them by 
efferent vessels which pass into the kidneys. 

(b) The corpora adiposa or fatty bodies lying in front of the kidneys. 

(c) The ureters which run along the outside of the kidneys and unite 

posteriorly to form a single duct opening into the cloaca. 

[In the Frog the ureters do not join together but open separately into the 
cloaca. Each ureter has a slight swelling, the vesicula seminalis, on its outer side.] 




—Testis 



Kidney 




Corpora 
" adiposa 



Ureter 



"Vesicula seminalis 



Bladder 



Fig. 9— Male Urinogenital System of Xenopus and Rana. 



26 



In the female Platana note : — 

(a) The ovaries, a pair of irregularly-lobed organs usually consisting of 

a mass of rounded black and white bodies, the ova. The 
ovaries are attached to the dorsal wall of the body cavity by a 
fold of the peritoneum. 

(b) The corpora adiposa lying in front of the kidneys. 

(c) The long convoluted oviducts opening into the body cavity in front 

and into the cloaca behind. 

The ureters open separately into the cloaca in the female. 
Make a drawing of the urinogenital system. 



Ovary 



Oviduct H 




-Corpora 
adiposa 



Ova --• 



Oviduct -- 



Ureter 




Ovary- 



Corpora 
adiposa 



Fig. 10. — Female Urinog-enital System of Xenopus and Rana. 



28 



Fifth Day. 
Skeletal System {continued). 

A. The Pectoral and Pelvic Girdles and Limbs. 
1. Detach a fore-limb with the remaining parts of the pectoral girdle. 
Make a preparation showing these various parts : — 

Supra-scapula, scapula^ remainders of the clavicle and the coracoid, 
humerus, radio-ulna, carpal bones, and digits. Draw these parts. 







Supra 


scapula 






\. Oroosterniim 




Scapula 


0k 




lg^ 


Scapula 


.Clavicle I 


:. - Episternum 


gtfvfl 




1 

5>\;/.y Supra- 




. .^ 




^^] 


I Zf Glenoid cavity 




Coracoid ^ 
- Epicoracoid 


^i/ scapula 






Coracoid' \Ji 


W- Epicoracoid 

IL Sternum M ^ 


tasternum 


Metasternum 












^\ -Xiphisternal!! 





Fig. 11.— Pectoral Girdle of Xenopus and Rana. 

2. Detach the pelvic girdle from the transverse processes of the 9th 
vertebra. Remove it with the hind-limbs from the body. Detach the femur 
from one side of the pelvic girdle, and make a sketch showing the following 
parts of the pelvic girdle : — Acetabulum, ilium, ischium, and pubis. 



Acetabulum 



Acetabulum 



Ilium 




Ischium 




Pubif 



Fig. 12.— Pelvic Girdle of Xenopus and Rana. 

Make a preparation and a sketch showing the femur, tibia-fibula, 
astragalus, calcaneum and the other bones of the tarsal region, five meta- 
tarsals, and digits. Number the digits from the inner side. 




Fig. 13. — Hind and Fore Limbs of Xenopus. 
30 



B. The Vertebral Column. 

i. Remove the skin and muscles from the dorsal surface of the back to 
show the nine vertebra? and the urostyle. Make a drawing showing the 
vertebras with their transverse processes, and the urostyle attached to the 
posterior end of the 9th vertebra. 



Atlas 
- Axis 




■Transverse process 
Cartilaginous rib 



Transverse process 
of 9th vertebra 



Urostyle 




.Transverse 
process 



Transverse process 
of 9th vertebra 



Urostyle 



Fig. 14.— Vertebral. Column of Xenopus and Rana. 



The 2nd, 3rd and 4th vertebra? bear long transverse processes curved 
backwards, those of the 3rd and 4th being tipped with small cartilaginous 
ribs. The transverse processes of the 5th, 6th, 7th and 8th vertebra? are 
slender and project forwards and outwards. The 9th vertebra has long 
flat wing-like processes attached to which are the ilia of the pelvic girdle. 
The urostyle is fused to the 9th vertebra. 

[In the Frog the transverse processes are produced outwards and they do 
not bear cartilaginous ribs. The urostyle is attached to the 9th vertebra by two 
facets.] 

Note the intervertebral foramina for the exit of the ' nerves from the 
spinal cord, and the intervertebral discs. 



32 



2. Remove, examine, and draw the 1st or atlas vertebra, note its ring-like 
form, absence of transverse processes, the concave facets by which it articu- 
lates with the two occipital condyles of the skull. 

3. Remove, examine, and draw the 3rd vertebra and note the opisthoccelous 
centrum, neural arch and neura! spine, anterior and posterior zygapophyses, 
the transverse processes, and the cartilaginous ribs. 

[The centrum is procoelous in the Frog and there are no ribs.] 

4. Remove and examine the 8th vertebra and note that the centrum is 
opisthoccelous. Make a drawing of a section showing the centrum. 

[In the Frog the centru/m is amphicodous .] 

5. Remove and examine the 9th vertebra or sacrum, and note that the 
centrum is slightly convex on the anterior surface. The urostyle is fused to 
the posterior surface of the 9th vertebra. Note also the long flat wing-like 
trans v T erse processes. 

[In the Frog the centrum is also convex anteriorly and on the posterior surface 
there are two convex facets for the articulation of the urostyle.] 



34 



Sixth Day, 



Skeletal System (continued). 

C. The Skull. 

1. Remove the skin and other tissues from the top of the skull and observe 
the large fronto-parietals, nasals, supra-ethmoid, premaxillse, maxillae, 
squamosals, exoccipitals, and pro-otics. The quadrato-jugals are very 
inconspicuous. The extrastapedial plate of cartilage is well marked and 
the bony columella may be seen lying underneath it. The sides of the skull 
are ossified and may represent the orbitosphenoids and alisphenoids of higher 
types. The supra-occipital consists of a piece of cartilage. 



Supra-ethmoid 




Squamos 




Occipital condyle- ; I 

Fo-amen magivj 



FiG. 15. — Dorsal view of Skull of Xenopus and Rana. 



[In the Frog there is no supra- ethmoid present, but a sphenethmoid closes 
the front of the cranial cavity. The sides of the skull are cartilaginous. A 
quadrato-jugal is well marked, but the quadrate consists of a piece of cartilage 
at the posterior end of the quadrato-jugal between the pterygoid and the squamosal. 
The lower jaw articulates with it. The columella is usually not well shown.'] 

Make a drawing of the dorsal side of the skull. 

36 



2. Remove the skin from the roof of the mouth and note the parasphenoid 
and single vomer, pterygoids, which are large and send leaf-like processes 
towards the middle line covering the Eustachian passages, squamosals, 
quadrates, basi-occipital, ex-occipitals, premaxillse, and maxillae. The 
orbitosphenoid and alisphenoid are well marked. There are no palatines 
present. 




Maxilla 
-Orbitosphenoid 



SpheTietnmoid 



-Squamosal 



Exoccipital-' 



Basi-occipital 




Ouadrato-;uga ! 



Exoccip 



FiG. 10. —Ventral view of Skull of Xenopus and Rana. 

[In the Frog there are a pair of vomers bearing the vomerine teeth, palatines, 
and quadrato-jugals. The pro-otics, which are not seen in a ventral view of 
the skull in the Platana, being covered over bij the pterygoids, are shown in the 
Frog.] 

Make a drawing of the ventral side of the skull. 



Orbitosphenoid Frontoparietal Alisphenoid 
Supraethmo 

Ni 



Frontoparietal 




P.Ieii>oflneek.elian- 



FiG-. 17. — Side view of Skull of Xenopus and Rana. 

3. Make a drawing of the bones of the skull viewed from the posterior 
end, showing the occipital condyle at each side of the foramen magnum, 
ex-occipitals, basi-occipital, supra-occipital, pro-otics, columella, and quadrate. 

[In the Frog the basi-occipital and supra-occipital are not developed.] 

4. Remove the skin from the lower jaw and make out the bones sur- 
rounding the original Meckel's cartilage, viz., the mento-meckelian, dentary, 
and articular. 

[In the Frog the lower jaw is composed of the mento-meckelian, dentary and 
angulo-splenial.] 

Make a drawing of the lower jaw. 



38 



Nervous System. 

A. The Central Nervous System. 

The Brain. 

Carefully remove the fronto-parietals so as to expose the brain, and note 
the following parts : — 

(a) The olfactory lobes, forming the most anterior portion of the brain, 

united together in the middle line. Anteriorly the olfactory nerves 
are given off. 

(b) The cerebral hemispheres, a pair of smooth elongated bodies. 

(c) The thalamencephalon, lying immediately behind the cerebral 

hemispheres. It is covered by the choroid plexus, a thick vascular 
membrane, and gives rise dorsally to the stalk of the pineal body. 

(d) The optic lobes, a pair of oval bodies. 

(e) The cerebellum, a narrow transverse band immediately behind the 

optic lobes. 

(/) The medulla oblongata behind the cerebellum. It gradually tapers 
towards its posterior end, where it is continuous with the spinal 
cord. On its roof the pia mater forms a very vascular choroid plexus. 

Make a sketch of the brain. 



40 



Seventh Day. (Revision.) 



With a second specimen revise the second, third, and fourth days' work, 
paying particular attention to the vascular system. 



42 






Eighth Day. 



Nervous System {continued). 

B. The Peripheral Nervous System. 

1. The Spinal Nerves. 

Remove the abdominal viscera carefully so as to expose the spinal nerves 
which are seen as white cords on each side of the vertebral column as follows : — 

(a) The first or hypoglossal nerve arising between the 1st and 2nd 

vertebra?. It runs forwards on the under surface of the head beneath 
the mylo-hyoid muscle and supplies the tongue. It was noted in 
the third day's work. 

(b) The second and third nerves unite immediately after escaping from 

the spinal cord to form the brachial plexus, which supplies the 
muscles of the shoulder, and then extends along the arm. 

(c) The fourth, fifth, and sixth nerves are small and supply the muscles 

and the skin of the body wall. 

(d) The seventh, eighth, and ninth nerves run obliquely backwards, the 

eighth and ninth uniting to form the sciatic plexus, which gives 
rise to the large sciatic nerve which extends along the thigh, and 
down the leg. The sciatic plexus also receives a branch from the 
seventh nerve. 

(e) The tenth or coccygeal nerve, which escapes through a small aperture 

in the side of the urostyle, and is distributed to the walls of the 

cloaca and urinary bladder. It is connected by a branch with the 

sciatic nerve. This nerve is frequently small or absent in the 

Platan a. 

[In the Frog, the seventh, eighth, arid ninth nerves unite to form the sciatic 

plexus which gives rise to the large sciatic nerve extending along the thigh, and 

dividing above the knee into the tibial and peroneal nerves to the leg and the foot. 

The tenth nerve is present.] 

2. The Sympathetic Nervous System. 

This system consists of a cord on each side closely following the course 
of the systemic arches and the dorsal aorta. It has on it six ganglionic 
swellings, and there are connections between the ganglia and all the spinal 
nerves. Anteriorly each of the cords is joined to the vagus nerve ; it ends 
posteriorly as a broad swelling on the ninth spinal nerve. 

[In the Frog the system consists of a chain of ganglia on each side of the 
body closely following the course of the systemic arches and the dorsal aorta. 
The cords have connections with the spinal nerves. Anteriorly each cord ends 
in the Gasserian ganglion of the trigeminal nerve and posteriorly it is united 
with the coccygeal nerve by a varying number of branches.] 

Make a complete sketch showing the spinal nerves and the sympathetic 
nervous system, 

44 



3. The Cranial Nerves. 

Expose the brain and note the following cranial nerves : — 

(a) The olfactory nerve, arising from the anterior end of the olfactory 

lobes, supplying the olfactory capsule. 

(b) The optic nerve, arising from the ventral surface of the brain below 

the optic lobes, supplying the retina of the eye. 

(c) The trigeminal nerve, arising just behind the optic nerve, giving 

rise to the following branches : — 

(i) The ophthalmic nerve, which passes over the muscles of the eye 

and supplies the skin in the region of the olfactory capsule. 
(ii) The maxillary nerve, which runs . forward under the eyeball, 

and supplies the skin covering the upper jaw. 
(hi) The mandibular nerve, which is at first continuous with the 

maxillary, and then bends round the inner surface of the upper 

jaw to extend along the outer surface of the mandible. 



Brachial plexus 




Glossopharyngea 
nerve - - 



Lingual artery 
Hypoglossal nerve 




Spinal 6- 
Dorsal aorta- 
Spinal 1- 
Sciatic plexus Spinal 8 
Spinal » 



Glossopharyngeal 

nerve |- 

Vagus nerve" 



.Cerebral 
hemispheres 

-Thalamencephalon 

Optic lohes 
Cerebellum 

Medulla oblongata 



Hypoglossal 
(1st spinal nerve) 



Fig. 18. — Brain. Cranial Nerves. Spinal Nerves, and Sympathetic Nervous System of 

Xenopus and Rana. 



(d) The glossopharyngeal and the vagus (or pneumogastric) nerves, 
leaving the skull together, immediately behind the auditory capsule. 
The glossopharyngeal passes along in front of the hypoglossal nerve 
and proceeds along the base of the tongue. The vagus, after giving 
off branches to the dorsal muscles, reaches the walls of the pharynx 
and run obliquely backwards to supply the pharynx, heart, lungs 
and stomach. 
Make a complete sketch showing the brain and the above-mentioned 
cranial nerves. 

46